1. Field of the Invention
The present invention relates generally to methods and devices for cannulation and, more particularly, to an intravascular cannulation assembly having at least two flow paths slidably coupled to one another suitable for use in a variety of cardiac procedures.
2. Description of Related Art
Cannulas and cannulation techniques are used in medical applications for transporting fluid into or out of the body. An area of proliferated use is cardiac surgery, where cannulation is routinely employed to transport fluid into, out of, or between various points in the circulatory system. This may be done for the purpose of performing cardiac procedures including, but not limited to, cardiopulmonary bypass (CPB), as well as left-heart and/or right-heart assist procedures.
The role of cannulation in cardiac surgery may be described by way of example with reference to coronary artery bypass graft (CABG) surgery. CABG surgery involves connecting a source of arterial blood downstream from a narrow or occluded section of a coronary artery for the purpose of providing an improved supply of oxygenated blood to the vasculature of the heart. The source of blood is often an internal artery, and the target is typically among the anterior or posterior coronary arteries. CABG surgery may be either open chest or closed chest (minimally invasive). Open chest CABG involves performing a sternotomy to spread the chest apart and provide access to the heart. Closed chest CABG surgery involves accessing the heart through conduits extending into the chest cavity, such as by thoracotomy. CABG surgery may also be performed on a stopped heart or a beating heart.
During stopped heart and beating heart CABG surgery, it is necessary to provide additional circulatory support in order to maintain the hemodynamic stability of the patient. For stopped heart CABG surgery, this is accomplished by establishing full cardiopulmonary bypass (CPB), wherein blood is diverted from the lungs for artificial oxygenation at a remote location. This may be referred to as providing “full” cardiac support. For beating heart CABG surgery, this is preferably accomplished by providing right-heart and/or left-heart assistance, wherein blood is rerouted from one location in the heart to another under the direction of a blood pump so as to obviate the need for an artificial oxygenator, filter, tubing, saline, etc. This may be referred to as providing “partial” cardiac support. Rerouting the blood during beating heart surgery may also serve to unload a selected chamber of the heart in an effort to stabilize the tissue and thus make it easier for the physician to perform the grafting procedure.
The process of placing a patient on full or partial cardiac support is conventionally accomplished using two cannulas. In stopped heart CABG surgery, the first cannula is placed in the right atrium as an inflow or suction cannula, while the second cannula is placed in the aorta as an outflow or return cannula from the oxygenator. In beating heart CABG surgery, the first cannula may be placed in the right or left atrium, and the second cannula placed within the aorta or pulmonary artery depending upon what side of the heart is being assisted. In either case, placement of the cannulas may be direct or indirect. Direct cannulation involves introducing the cannula directly into the desired heart chamber or major vessel extending directly from the heart (i.e. aorta or pulmonary artery). Indirect cannulation involves advancing the cannula intravascularly into the desired heart chamber or major vessel extending directly from the heart (i.e. aorta or pulmonary artery).
Direct cannulation systems of the prior art suffer a variety of drawbacks. A first drawback is that cannulation can only be performed so long as the chest cavity is maintained open. Another drawback is that introducing the cannulas and related tubing through the chest cavity reduces the field of surgery, that is, the amount of space within which the surgeon has to operate. In addition to reducing the field of surgery, the surgeon must make separate incisions for each cannula, with each incision presenting a potential site for leakage and infection. Direct cannulation through the chest cavity also lengthens the overall time required to perform a CABG procedure because the surgeon must personally position each cannula after opening up the chest cavity. This increases the overall time that the patient's chest will be open and exposed to atmosphere. It is also more costly and ties up valuable hospital resources (i.e. beds, staff, etc . . . ) for a longer period, which can be especially troubling in emergency room situations where a limited number of beds and staff are commonplace.
Indirect cannulation overcomes many of the above-enumerated drawbacks associated with direct cannulation. Indirect cannulation advantageously provides the ability to perform closed chest cardiac surgery in that a sternotomy is not required to access the heart. Indirect cannulation can also be maintained well after the given cardiac procedure is completed. This is advantageous in providing continued circulatory support after a procedure has been completed, as well as providing the ability to close the chest following open chest surgery without jeopardizing cannulation. Indirect cannulation also reduces the clutter from the field of surgery so as to avail more space for the surgeon. It provides the ability to have someone other than the physician establish cannulation. In so doing, indirect cannulation allows the doctor to perform the cardiac procedure in the least amount of time, thereby reducing cost.
While indirect cannulation presents significant improvements over direct cannulation, the prior art indirect cannulation systems are nonetheless flawed. One disadvantage of prior art indirect cannulation systems is that the cannulas are rigidly fixed to one another and thereby do not provide any degree of adjustability between the distal ends of the cannulas. This severely restricts the ability to place a particular cannula assembly in the appropriate locations in the circulatory system. In so doing, it will result in much guess-work in selecting a cannulation assembly of the appropriate size. Inefficiency in selecting and placing an appropriately sized cannulation assembly translates into increased costs, both in terms of hospital resources (i.e. beds, staff, etc . . . ) as well as the unnecessary costs associated with discarding cannulation assemblies that were introduced into the circulatory system and later found out to be inappropriately sized for the intended cardiac support function. Prior art indirect cannulation systems are also limited in terms of their flow characteristics.
The present invention is directed at eliminating and/or reducing the effects of the foregoing drawbacks of prior art.